1. Field of the Invention
The present invention relates generally to surface acoustic wave signal processors and more specifically to surface acoustic wave signal processors that are relatively insensitive to ambient temperature variations.
2. Description of the Prior Art
Signal processors for surface acoustic waves are well known in the art. Typical of such signal processors are the reflective array devices used as band pass filters or pulse compression filters. Such filters are constructed on a piezoelectric substrate on which are formed input and output transducers and in which one or more reflective arrays are positioned obliquely in the propagation path between the input and output transducers. Each reflective array contains a group of parallel grooves oriented so as to provide a reflected signal nominally at right angles to the signal incident on that array.
Typical of such prior art processors are devices in which the input transducer launches a wave along the Z axis of the crystal and a single reflective array reflects the beam along the X axis toward the output transducer.
Processors of this type are described, for example, in U.S. Pat. No. 4,055,820, issued in my name on Oct. 25, 1977 and assigned to the present assignee.
Variants of the above-described signal processors are also known in the art in which a pair of arrays are positioned so as to effectively reverse the direction of a launched wave and thereby provide a U-shaped propagation path.
Still another variant of the signal processor which is known in the prior art includes a first reflective array for reflecting the wave as launched by the input transducer at a right angle to the launched wave, and a second array for again reflecting the wave at a right angle so that after the second reflection the wave propagates toward the output transducer in the same direction as the originally-launched wave.
As will be explained, the characteristics of each of the above-mentioned processors are greatly influenced by the ambient temperature. The solution to the problem until this time has been to keep the substrate in a temperature controlled oven. However, this may not always be an acceptable solution because of factors such as size, cost or power requirements of the oven.
The present invention provides a means for overcoming the temperature dependency of such signal processors while at the same time minimizing the overall length of the substrate on which the processor is formed.